The present invention relates generally to body-mounted camera stabilizing devices which are adapted to isolate devices such as a camera from the unwanted angular and spatial motions of an ambulatory operator. This is done to permit smooth moving camera shots over rough ground, up stairs, and the like.
Such devices are generally comprised of a camera equipment support structure, gimbaled at its center of gravity and supported by an equipoising structure attached to a vest worn by the operator. Camera stabilizers of this kind have long been in use and have become a staple of the motion picture and video industries. The Steadicam.RTM. camera stabilizing device received an Oscar in 1978. This device is described in U.S. Pat. Nos. Re. 32,213; 4,156,512; and 4,474,439. A support arm for use in conjunction with this device is further described in U.S. Pat. Nos. 4,208,028 and 4,394,075. For further details, reference is made to these patents, which are incorporated by reference as if fully set forth herein.
Camera stabilizers such as these typically employ a three-axis gimbal at the point of attachment to the camera equipment support structure which provides the desired degree of isolation from the operator. It is necessary to position the camera components and their support structure (i.e., camera equipment) such that the static center of gravity of all of the components is located approximately at the common centers of rotation of the axes of the gimbal. The relatively massive camera is itself counterbalanced by the other (rigidly attached) components, and is supported in approximately neutral balance. The camera can thus be aimed in any direction by a slight pressure of the hand adjacent to the gimbal. The directions of these aiming motions are distinctly referred to as pan, tilt and roll.
As used herein, "roll" is defined as rotation about an axis parallel to that of the camera's lens. "Tilt" refers to rotation about an axis which is horizontal, but offset 90.degree. from the axis of the lens. "Pan" means rotation about an axis parallel to that of "true vertical" (i.e., rotation around a line to the gravitational center of the Earth, which is not necessarily related to the momentary tilt angle of the camera, which may then be tilted).
To achieve an enhanced result, the present invention includes improvements to several aspects of the camera equipment support structure. The support structure (also known as the "sled") includes improvements to its so-called upper stage (the top portion of the camera support which includes camera attaching hardware and means for adjusting the camera's fore-and-aft and/or side-to-side position), to its lower portions (which include the video monitor, the battery, their attaching hardware, and the associated electronics and wiring), and to its support structures (including the center post, gimbal and handgrips). Also provided are improvements in the handgrip associated with the gimbal, on the operator's side, and the center post and gimbal which support the "sled".
For some time, the technique of operating camera stabilizing supports has been refined so that a skilled practitioner can make and control rapidly panning shots. As the speed of this rotation increases (at times beginning from rest, sweeping 180.degree. or more, and coming to a stop in less than a half second), the dynamic balance of the spinning mass becomes crucial to retaining control over the camera's attitude at the end of the pan. Consequently, an important goal is to help operators with the complex requirements of dynamic balance. Various articles have been published describing empirical methods for achieving dynamic balance in order to permit operators to make such rapid pans without gyroscopic "precession" which can cause the camera to seek a different tilt or roll angle when spun. Articles have also been published setting out the mathematical basis for the dynamic balance of a camera stabilizing support, including G. Brown, "Trim", Steadicam Letter, Vol. 1, No. 1 (Spring, 1988), and A. DiGiulio, "Trim-II, The Sequel", Steadicam Letter, Vol. 1, No. 2 (Summer, 1988, which are incorporated. by reference as if fully set forth herein. A number of modifications and after-market accessories have also been developed to permit the lower sled components to move into the positions required for dynamic as well as static balance of the system.
Unfortunately, the average operator still generally relies on guessing or trial and error (with empirical "spin-test" rigs) to achieve this desirable condition. What is more, any subsequent change to the camera equipment configuration, such as raising the monitor, not only degrades dynamic balance but also alters static balance. This requires the operator to raise or lower the vertical position of the gimbal to restore balance. Neither the few operators who are comfortable with the empirical balancing methods, nor the fewer yet who understand the mathematics involved, have the time necessary to deal with problems of dynamic balance in the middle of a "shoot". The addition and removal of accessories still further complicates the situation. As a result, and most of the time, such camera stabilizing supports are not dynamically balanced, and are therefore liable to precession during rapid panning shots.
The technique of operating camera stabilizing supports has also been refined so that a skilled practitioner can execute moving shots which may be indistinguishable from those made with wheeled camera dollies. However, the hardware itself has only been improved incrementally. For example, U.S. Pat. No. 4,474,439 discloses a sled having additional flexibility for arranging the camera equipment components in order to execute various kinds of shots, and various practitioners have improved upon its ease of use. However, a number of quite fundamental operating problems relating to the structure of these devices still have not been fully resolved.
One important goal is to help operators with the frequent requirement for "trimming" of the camera. Adjusting the position of one or more components of the gimbaled camera equipment will alter its nominal balanced angle. Trimming currently requires touching the gimbaled mass of the camera equipment (which is freely rotatable in three axes), which inevitably causes it to swing back and forth. As a result, the operator must make an adjustment, counteract the camera's induced (unwanted) motions by hand, and wait for the system to settle down to ascertain if the adjustment has had the desired effect (such as to level the camera, or otherwise alter its angle). Any attempt to manually "trim" the camera's balance during a shot results in unwanted angular motions that are easily visible when viewing the results. Operators have therefore had to make do during a shot with a preselected, fixed "trim" and have had to work against the unit's fixed trim during any portion of the shot that required a different camera attitude.
Also to consider is that camera stabilizing supports exhibit a moment of rotational inertia in their pan axis, based upon the fore-aft distribution of the system's masses. This value is not subject to the operator's control, despite the fact that certain shots (such as slow moving shots with a minimum of panning) would benefit by the ability to increase this moment to provide greater inertia, and thus, stability. On the contrary, rapidly panning shots would benefit by a reduction in the moment of rotational inertia to reduce the torque needed to rapidly spin and/or stop spinning this relatively large mass.
An exact, "neutral" balance of the camera equipment is seldom employed by operators because it provides no tendency to cause the camera equipment to remain upright, and therefore requires constant vigilance in order to keep the camera level in the roll axis. This means that attention would have to be diverted from the content of the shot to accomplish this task. In practice, it has been found that displacement of the center of gravity slightly downward from the center of the gimbal (typically accomplished by raising the gimbal about one-quarter inch up the center post which connects the top and bottom masses of the camera equipment) provides a very slight bottom-heaviness which causes the camera to weakly seek a level attitude in tilt and roll. This arrangement has been found convenient, and contributes to the operator's ability to repeatably execute shots.
If, in addition, the camera's fore-aft balance is altered (e.g., offset slightly forward from the level neutral position), it will have a tendency to remain tilted slightly downwardly throughout the shot. This fore-aft balance can be adjusted to help preserve a desired tilt angle, and seek a given framing (i.e., "headroom" for an actor following at a given distance). Unfortunately, this also cannot be accomplished during shooting. The camera equipment is so freely balanced that even a light touch by the operator or an assistant (anywhere other than adjacent the gimbal, at the center of gravity), would disturb the shot. For this reason, camera assistants generally employ radio-controlled servo motors to adjust the camera lens (or other parameters) so as not to touch the camera. It has been found that even light gauge wires connected to the camera will exert an undue influence and reduce the operator's independence of motion.
Problems arise when a shot requires a series of complex moves which include serial changes in the camera's desired tilt. Once again, operators had to select a single trim setting (which could not be changed while shooting) in order to accommodate the most difficult section of the shot (such as a long hold at the end, or a block or two of walking just ahead of an actor). When changes in the tilt angle were required, the operator had to maintain a continuous pressure on the "handle" section of the center post in order to maintain this different angle. When extremes of tilt are serially required, portions of shots inevitably included some visible spurious motion.
These variations in the amount of force required to maintain tilt angles that were not "trimmed-for" often produced slight "swimming" motions (up and down) and also degraded the operator's control of the remaining axes.
Another problem for operators of these devices relates to the difficulty in maintaining the camera level enough so that the framing is correct relative to vertical objects seen in the background of the shot. Although a slightly bottom-heavy camera equipment will tend to seek level when the camera is stationary, it is nevertheless pendular and will react to lateral accelerations and decelerations with a slight tendency to depart from level. This must again be counteracted with subtle hand pressure on the "handle" portion of the support. Incorrect compensation yields shots which are sometimes mis-framed or off-level. In any event, it is a compromising arrangement. The level-seeking properties are desirable, but considerable skill is required to deal with the pendular consequences.
Attempts have been made to adapt wireless control of the camera's "roll" attitude (e.g., by a motorized roll-cage swivelled to permit a second party to slowly "bank" the camera during a tracking shot) to simulate flight. Attempts have also been made to automate camera leveling responsive to an electronic level sensor (e.g., by tilting the camera itself to compensate for an off-level condition of the camera support). However, the degree of tilt had to be tuned to each individual camera weight and shape, and such efforts proved to be unproductive. In order to overcome the imbalance caused by the lateral shifting of film weight in co-axial film magazines, attempts have been made to compensate for translations of weights and/or camera equipment using clockworks or motors and lead screws. These efforts also proved to be unproductive because the required rate of movement tends to vary according to the prevailing degree of bottom-heaviness of the gimbaled camera equipment.
Further complicating matters is that operators have not been able to achieve precisely graduated, or even repeatable alterations of the camera equipment's degree of bottom-heaviness. The principal reason for this is that the gimbal is traditionally fixed to the center post of the camera stabilizing support with a clamp. To change the location of the gimbal, the operator needed to loosen the clamp while holding the equipment in a sideways attitude so that the freed gimbal would not slide uncontrollably to one end or the other of the post. Once the gimbal was moved, the clamp was re-tightened and the usual test (the "drop" test) was performed to check for the pendular period of the gimbaled mass. Most film cameras employ a vertical film transport, within the magazine, which shifts about 1.5 pounds of film downwardly about four inches during the average four-minute duration of a film magazine. To date, it has not been practical, or even possible to accurately compensate for the resulting, progressive increase in bottom-heaviness.
In addition, shots that require extreme tilts are easier with less bottom-heaviness. Straight-ahead, level shots or shots made in windy conditions are more stable with more bottom-heaviness. Extendable center posts have been used to provide additional length for counterbalancing even the heaviest of cameras. However, each change in post length requires an adjustment of the gimbal to re-establish balance. Each change of the lens (from a light to a heavy lens) alters the degree of bottom-heaviness, as well. All of these situations would ordinarily indicate a need to adjust (move) the gimbal. However, too often, operators must endure inappropriate degrees of bottom-heaviness to save time and effort.
Also to consider is that prior gimbals employed two large rotational bearings, with the yoke pivot bearings located within the yoke ring. This caused the yoke ring structure to be of a size that prevented the operator from grasping the gimbal more closely to the center of gravity. In addition, previous gimbals suffered from inexact centering due to the distorting nature of the clamping mechanism. Inexact centering can cause the camera to change its angle slightly as its orientation relative to the operator varies.